It is known in the medical profession that the heartbeat of a normal fetus has associated with it a frequency which varies between statistically acceptable limits, the amount and direction of this variation also having certain pronounced characteristics. Variations in heart beat frequency patterns and/or deviations in such patterns from a norm can be correlated with occurrences of fetal distress caused either by some infirmity internal to the fetus or by external forces applied directly to various parts of the fetus anatomy or to the umbilical cord, such external forces often being attributable to maternal uterine contractions during labor.
Physicians have monitored fetal heartbeat using stethoscopes to determine fetal condition. This method of fetal heart rate monitoring is a severely limited one due to shortcomings in the ability of an individual to instantaneously analyze the information transmitted to him and to detect subtle characteristics of the fetal heartbeat pattern. The importance of continuous fetal heart rate monitoring and the shortcomings of evaluation by stethoscope are discussed in "An Introduction to Fetal Heartrate Monitoring", by Edward H. Hon, M.D., published by the Postgraduate Division, University of Southern California, School of Medicine, Los Angeles, California. This publication also discusses problems associated with the monitoring of fetal heart rate caused by interference associated with uterine contractions during labor.
In order to provide an accurate and complete picture of the fetal heart rate pattern, it is known to record heart rate as a function of time with the pattern displayed on a cathode ray tube device or plotted on a strip chart recorder. (See U.S Pat. No. 3,599,628 of Abbenante for "Fetal Heartrate and Intra-Uterine Pressure Monitor System"). Monitoring apparatus of this type permits a physician to analyze fetal heart rate and uterine contraction patterns and the correlation therebetween to determine fetal condition. However, such analyses require the judgment of specially trained physicians and cannot be done practically on a continuous basis. Furthermore, the results of such time consuming analyses, when performed, may become available too late for meaningful corrective action. It is therefore desirable to monitor parameters of fetal condition continuously and instantaneously with provision for alerting cognizant medical personnel as soon as possible of the onset of fetal distress.
Although current technology is available for comparing measurements expressed in quantitative form with quantitative tolerance limits and signaling when those limits are exceeded, the evaluation of fetal heart rate and maternal uterine contraction patterns has until now often been a qualitative one beyond the capabilities of the heretofore known state of the art. Thus, in order to achieve the advantages of instantaneous and continuous monitoring and alerting, and comprehensive analysis of fetal heart rate and maternal uterine contraction patterns, it is necessary to devise apparatus capable of performing timely and comprehensive pattern analyses and expressing the results of such analyses in quantitative parametric form capable of comparison with a standard of normalcy so that the onset of a fetal distress condition may be immediately known.